附有周期项的预报模型及其在GPS卫星钟差预报中的应用研究

为了有效进行GPS卫星钟差预报和更好地反映卫星钟差特性,除了考虑卫星原子钟频移、频漂和频漂率等物理性质外,还应考虑到卫星钟差的周期性变化特点.在二次多项式模型基础上,增加了周期项因素,构造了新的预报模型.选取部分GPS卫星铯钟(Cs.clock)和铷钟(Rb.clock)钟差资料,根据钟差变化趋势分3种情况,按不同时间长度进行钟差预报分析,并与二次多项式模型的预报结果比较分析,大量数据分析表明:附有周期项的二次多项式模型预报精度优于二次多项式模型,铷钟预报精度略优于铯钟.     

基于修正线性组合模型的原子钟钟差预报

原子钟钟差预报在时频工作中起着重要作用.目前常用的预报模型各有优缺点,为了综合各种预报模型特点,可以考虑组合这些模型预报的结果.针对线性组合模型预报钟差时存在的问题,提出了学习权的概念,以有效地利用各种精度信息,建立了修正组合预报模型.为了验证该方法的有效性,选取了4颗GPS卫星IGS(International GN...     

A Research on the Algorithm of Local Atomic Time

The goal of all time laboratories’ pursue is to produce and keep a stable, precise and reliable time scale. The long-term stability of the time scale is mainly taken into account in the traditional ALGOS algorithm, while the local atomic time scale should give consideration to both the long-term and shortterm stabilities. From the analysis and research on the atomic clock noise model and under the condition that the long-term stability of the local atomic time scale does not drop, a complete algorithm is proposed which is suitable for the calculation of the local time scale TA (NTSC) carried out at the time laboratory with the time-keeping clocks of a unitary type and being close in performance at the National Time Service Center, called the NTSC for short, of Chinese Academy of Sciences. The data of all the clocks in the NTSC which participated in the calculation of the International Atomic Time (TAI) all the year round in 2008 are applied to the test and verification of the new algorithm, with the result showing that both the short- and long-term stability indexes of the obtained TA (NTSC) are improved. The research result is suitable for the calculation of the atomic time scale of the time laboratory whose time keeping system is similar to that of the NTSC.     

北斗系统测站钟差短期预报模型比较及其在单星定轨中的应用

北斗卫星导航系统(BDS)地面跟踪站都配置有高精度的氢原子钟,并基于精密定轨数据处理与主站的时间基准进行同步.在卫星轨道机动以及机动恢复期间,通常采用几何法定轨以及单星定轨确定卫星的轨道.而在这两种定轨模式中,需要提供精确的测站钟差作为输入.为提高定轨的实时性,需要对测站钟差进行预报处理.分析了2次多项式模型、附加周期项模型、灰色模型3种模型对北斗地面跟踪站钟差短期拟合和预报的性能,并将钟差预报结果应用于单星定轨,同时还分析了不同预报钟差用于定轨的精度.试验发现,以上3种模型对6个测站钟差的平均拟合精度分别为0.14 ns、0.05 ns、0.27 ns,预报1 h的平均精度分别为1.17 ns、0.88 ns、1.28 ns,预报2 h的平均精度分别为2.72 ns、2.09 ns、2.53 ns.采用3种模型对测站钟差进行预报并用于单星定轨,采用附加周期项的钟差预报模型轨道3维误差最小,不同模型轨道径向精度差异在3 cm以内.以上结果表明,附加周期项的站钟拟合及预报模型在北斗系统机动期间的轨道恢复数据处理具有最好的效果.     

Prediction of Clock Errors of Atomic Clocks Based on Modified Linear Combination Model†

The prediction of the clock errors of atomic clocks plays an important role in the work on time and frequency. Each of the prediction models often used at present has its own merits and shortages. A combination of the predicted results obtained by means of these models can be used to synthesize the characteristics of various kinds of prediction models. In the light of the problem which occurs when the linear combination model is used to make the prediction of clock errors, the concept of learning weight is proposed and the modified combination prediction model is made by taking advantage of various kinds of pieces of accuracy information. For verifying the efficiency of this method the clock error sequences of the IGS (International GNSS Service) of 4 GPS satellites are selected and the predicted results of the quadratic polynomial and grey model are combined. The result shows that the modified model can further improve the stability and accuracy based on the guarantee of the reliability.     

将来最准确最稳定的钟——空间微重力钟

介绍了目前最准确的原子钟,描述了将来最准确、最稳定的钟——空间微重力钟,以及高精度空间组合钟的预期性能,还介绍了一些正在实施的高精度空间钟计划。     

一种微型化铷原子钟

报道了一种微型化铷原子钟,它采用一种新型陶瓷填充微波腔来减小物理部分体积,其铷光谱灯采用升压电路以实现快速点亮,整机电子线路采用低电压技术,在国内首次对这类铷钟实现12V直流供电,并且首次对这类铷钟加入与外秒同步的功能。该铷原子钟体积为190mL,开机3min后可实现锁定,锁定后频率稳定度为1．5×10^-11／√τ（τ：1～1000s）,稳态功耗为5．5W。     

Research on the Method of Noise Error Estimation of Atomic Clockstwo

The simulation methods of different kinds of noises of atomic clocks are given. The frequency flicker noise of atomic clocks is studied by using the Markov process theory. The method for estimating the maximum interval error of the frequency white noise is studied by using the Wiener process theory. Based on the operation of 9 cesium atomic clocks in the laboratory of time and frequency primary standards of NTSC (National Time Service Center), the noise factors of power-law spectrum models are estimated, and the simulations are carried out according to the corresponding noise models. Finally, the maximum interval error estimates of the frequency white noises generated by the 9 cesium atomic clocks are acquired.     

北斗星地双向时频传递与广广播钟差精度分析

与其他卫星导航系统不同,北斗卫星导航系统采用星地双向时间比对技术,直接测量卫星钟相对于地面保持的系统时间的钟差,并用于广播电文钟差参数的建模。讨论了电离层延迟误差、卫星相位中心误差等不同误差源对不同类型卫星双向时间同步卫星钟差精度的影响。实测数据分析结果表明,星地双向卫星钟差内符合精度(RMS)优于0.15 ns。利用双向卫星钟差序列,对广播星历钟差参数预报精度进行了分析,统计结果显示广播电文钟差参数预报1 h,精度在2 ns以内,移动卫星刚入境时,钟差参数预报6 h误差可达10 ns。     

1998～2001年国家授时中心(NTSC)铯原子钟运转情况

主要介绍了用于保持中国科学院国家授时中心 (原陕西天文台 )时间尺度的 6台铯原子钟 (代号分别为 :Cs0 7、Cs0 8、Cs1 1、Cs1 6、Cs1 7、Cs1 8)的运行情况。 6台铯原子钟自 1 997年下半年正式给BIPM (国际权度局 )提供数据 ,参加国际原子时(TAI)计算至今已达 5年之久 ,在此期间 ,除Cs1 8因铯束管故障在 1 999年返回美国检修外 ,其它 5台钟运行情况良好。详细介绍、分析每台钟在 1 998～ 2 0 0 1年期间的整体特性、不同采样间隔下的稳定度比较、速率漂移以及它们在TAI系统中的取权情况。通过分析比较 ,使我们对每台钟的运行情况作出恰如其分的评价 ,以便更好地利用国家授时中心的钟资源 ,做好守时和授时工作。     

NTSC时频基准实验室守时系统自动监测软件

为了能实时了解中国科学院国家授时中心（NTSC）时频基准实验室守时系统的运转情况,编制了本软件。本软件的功能是对系统中原子钟最近一个月的比对数据进行实时计算后,得到一个纸面的加权平均时间尺度“TA”,用它作为监测UTC（NTSC）、UTC（JATC）和原子钟运转情况的参考,给出TA-UTC（NTSC）、TA-UTC（JATC）、以及每个钟相对于TA的速率曲线。通过选用窗体上设置的各个按钮,能很方便地监测原子钟和测量设备的运行情况。位于陕西蒲城的BPL监控室可以通过远程局域网得到NTSC守时实验室的数据,实时运行本软件,并用TA作为参考,即可监测BPL监控室原子钟运行情况,并且对BPL发播工作钟时间T（PU）进行监测和频率驾驭,以实现T（Pu）同步到扩形（NTSC）。     

脉冲星对氢原子钟的频率驾驭算法研究

氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟的频率驾驭,并对实时信号加以控制.首先分析了国际脉冲星计时阵(International Pulsar Timing Array,IPTA)第二批发布数据中四颗毫秒脉冲星的稳定度随时间的变化,同时采用哈达玛方差分析了中国科学院国家授时中心(National Time Service Center,NTSC)一台氢钟的频率稳定性能,最终给出了利用脉冲星驾驭氢原子钟频率的方法.     

第三代卫星导航定位系统星载原子钟的新发展

传统铷原子钟和铯原子钟已在卫星导航定位系统中作为星载原子钟获得重要应用.卫星导航定位系统的更新和新发展要求更高精度更小型的新型星载原子钟.该文介绍采用新物理原理和先进技术在下-代卫星导航定位系统有应用前景的新原子钟的产生和发展以及它们目前的进展.     

Comparison of BDS Station Clock Short-term Prediction Models and their Applications in Precise Orbit Determination

BDS (BeiDou Navigation Satellite System) ground tracking stations are equipped with high accuracy atomic clocks, and they are synchronized with the BDS time scale (BDT) via the Precise Orbit Determination (POD) processing. During the periods of satellite maneuver and post-maneuver, station clocks are kept fixed as known values in the POD processing. To improve the real-time POD capability, station clocks need to be predicted. In this paper, the performance of three clock prediction models is evaluated, including quadratic polynomial model (QP), periodical term model (PM), and grey model (GM). The precision of clock fitting and prediction, as well as the performance of the prediction models in POD are compared. Data of six stations are used for test, and the results show that: the mean fitting accuracy of quadratic polynomial model, periodical term model, and grey model is 0.14 ns, 0.05 ns, 0.27 ns, respectively; the 1 h and 2 h prediction precision of the three models is 1.17 ns, 0.88 ns, 1.28 ns, and 2.72 ns, 2.09 ns, 2.53 ns, respectively. Applying the 1 h and 2 h predicted station clocks in the POD, the 3D orbit accuracy reaches the best using the periodical term model, while the radial accuracy of satellite orbit is rather close for the three models with the difference within 3 cm.     

The problem of clock synchronization: A relativistic approach

The problem of synchronization of the Earth-based clocks has been discussed in the framework of General Relativity Theory. The synchronization is considered as the transformation of the observers' proper time scales to the coordinate time scale of local inertial geocentric reference system, which is single for all the observers. The formulas for the relativistic corrections occurring in some methods of Earth-based clock synchronization (transported clock, duplex communication via geostationary satellite and meteor-burst link, LASSO experiments) have been derived enabling one to attain the accuracy of 0.1 ns.     

用于JATC远程时间比对的双频GPS接收机

中国科学院国家授时中心为“我国综合原子时（JATC）建立与保持的研究”项目研制的双频多通道GPS时间传递接收机NTSCGPS-2，不仅具有远程时间比对的功能，还增加了我国综合原子时需要的本地钟比对功能和精密定位功能。在不增加其它比对设备的情况下，满足JATC项目对远程时间比对的要求。NTSCGPS-2具有如下性能特点：（1）采用双频观测，可实测电离层时延；（2）远程（西安-上海、西安-澳门）时间比对精度达到2ns；（3）具有本地钟间的比对功能，在正常共视观测的同时，还可进行2个本地钟间的比对；（4）具有精密定位功能，相对定位精度为5cm。     

Research on the Methods of Performance Monitoring and Evaluation for Active Hydrogen Maserstwo

Active hydrogen maser is the main frequency standard for establishing and maintaining the time scale. It has the characteristics of high short-term stability and low phase noise. At present, it plays an increasingly important role in the international atomic time (TAI) and various local time scales. Firstly, in combination with the internal state parameters of an active hydrogen maser, the correlation between the internal state parameters and the comparison data of a hydrogen maser is analyzed, and a method for the performance monitoring of a hydrogen maser is proposed. Secondly, according to the characteristics of hydrogen maser performance, a method for evaluating the performance of a hydrogen maser is given. The hydrogen maser performance includes mainly two aspects, namely the frequency stability and predictability. The performances of two types of active hydrogen masers (CH1-75 and MHM-2010) are evaluated by this method. The correlation analysis of the atomic clock state parameters and comparison data shows that the state parameter monitoring can effectively predict the variation of the hydrogen maser performance. The evaluation results of atomic clock frequency stability and predictability show that the atomic clock with a higher medium-and-long term frequency stability has a better predictability. There are two methods for the predictability evaluation, one is based on the data published by BIPM (Bureau International des Poids et Measures), and another one is based on the quadratic model. Both methods are consistent with the weights published by BIPM. Therefore, the two methods can be used as a quantitative method to evaluate the predictability of a hydrogen maser.     

原子钟信号的神经网络模型

时间尺度的连续性要求对原子钟信号进行必要的预测,预测的实质是建立一个模型来逼近原子钟的信号,前向神经网络具有良好的副近非线性 函数的能力,用神经网络模型来预测原子钟信号,并与AD模型的预测结果作了比较。     

网络技术在时间服务工作中的应用

主要介绍网络技术在授时中心守时实验室的守时及授时服务系统中的应用情况。守时系统是一种需要连续、可靠运转的复杂系统，包括守时钟组、比对测量系统、原子时归算等多个环节。原子时专用局域网是守时系统的一个重要的组成部分，它有效地提高了守时、原子时及相关数据资料的传递和交换速率。时间服务的网络化、自动化不仅有效提高了工作效率，减少了人工过多干预造成的误差，更重要的是可以提高守时系统的可靠性和合理性。章详细介绍原子时局域网络（ATLAN）系统和计算机网络授时系统的设计情况。     

氢原子频标的小型化

小型化是目前氢钟的发展方向之一，氢钟的小型化主要是谐振腔的改进，它的结构尺寸决定了氢钟的最小尺寸和重量，目前要用的小型腔主要有电极负载腔，磁控管腔，介质负载腔和TE111腔，新型的谐振腔虽然减小了体积减轻的重量，但量由于它本身已经很难满中立起振条件，所以在伺服电路上也不同于主动型氢钟，根据电路原理的不同，将小型化的氢钟分为反馈振荡型和被动型，反馈振荡型氢钟使激射器工作在反馈振荡状态，通过正反馈维持激射器振荡，被动型氢钟的激射器工作在振荡阈值之下，其作用与揩振放大器相似。